1. Field of the Invention
The invention relates to a system and arrangement for an electrothermal ink jet print head in a layer construction, where the extension direction of the electrothermally generated vapor bubble is directed opposite to the ink ejection direction.
2. Brief Description of the Background of the Invention Including Prior Art
Conventional electrothermal ink jet print heads, operating according to the bubble-jet principle, exhibit plurality of individual nozzles, where individual droplets of a defined size are generated under the influence of an electronic control, and wherein individual droplets are ejected according to a defined pattern in the direction of recording substrate.
The characters to be printed are in each case generated by a plurality of ink droplets, where the ink droplets are aligned like a matrix relative to each other.
Advantageously, in each case a column of such matrix referring to a production of characters is printed simultaneously in order to meet the requirements of a high print speed and of a uniform print image and of a uniform general impression.
An ink jet print head, which is suitable for the recited print method is to combine also several like elements, which are capable to eject the ink droplets at the required point in time i.e. the ink jet print head has to operate according to the "drop-on-demand" principle. It is a characteristic feature of this technology that an electric resistor, formed as a heating element, is disposed a capillary, filled with a recording liquid, such as for example ink, and in fact in the neighborhood of an opening of the capillary. If a certain thermal energy, generated by a short current pulse, is fed to this heating element, then a rapidly expanding ink vapor bubble is initially generated based on the extremely quick thermal transfer to the ink liquid, wherein the ink vapor bubble after a discontinuation of the energy feed and after cooling by the ink liquid collapses relatively quickly into itself. The pressure wave, generated in the interior of the capillary by the vapor bubble, induces and allows an ink droplet to be ejected out of the nozzle opening onto the surface of a closely neighboring recording substrate.
It is an advantage of this bubble-jet principle that the relatively large and quick volume change, necessary for the ink ejection, can be generated by way of a very small active converter face by employing the phase change liquid-gas-liquid of the ink liquid. The small converter faces in turn allow, in the context of an application of modern and present-day production methods, such as high-precision, photolithographic processes in layering techniques to provide a relatively simple and low-cost construction of ink jet print heads, which are characterized and distinguished by a high writing and recording track density and by small dimensions.
An ink jet print head is known from the international application PCT/DE/91/00364, which ink jet print head comprises essentially a chip and an ink-storage container, where the chip is mechanically clamped and attached on the ink-storage container by way of mounting clamps. This chip exhibits ink channels which are closed on three sides and open towards the fourth side, where the ink jet channels are separated from each other by thin, substantially trapezoidal intermediate channel walls. The closure of the respective ink jet channel is made of a thin membrane in the direction of ink ejection. The thin membrane in turn exhibits the ejection nozzle of the respective ink channel. A surface of the ink-storage container furnishes the outer closure of the ink channels toward the fourth side which is open toward the chip.
If a heating element is triggered and energized for the generation of a droplet, then the heating of the heating element leads to a local overpressure in the respective ink channel in addition to the vapor bubble formation. In addition to the intended droplet ejection, this overpressure leads to a situation where a certain amount and volume of ink is pressed backwards in the direction toward the supply channels. This means that, in addition to the amount of energy, required for the ejection of the droplets, there also has to be supplied an amount of loss energy amount, where the amount of loss energy is used, among other purposes for providing a back transport of the ink after termination of ejection. This amount of loss energy decreases the overall degree of effectiveness of the ink jet print head.
In addition, the pushed-back ink volume results in a local overpressure in the supply channels and thus in an influencing of neighboring ink channels. If the neighboring ink channels of a non-triggered ink channel are triggered and thereby driven, then there can nevertheless occur an undesired droplet ejection of the non-triggered ink channel based on the generated superpositioning of pressures accumulating in the non-triggered channel.
Depending on whether neighboring ink channels of a first channel are triggered and energized or not, the pressure conditions in the first ink channel change and as result the resulting droplet volume ejected from the first channel and thus the print quality change also.